In a radio receiver, especially a broadcasting radio receiver, if several signals are to be evaluated simultaneously, e.g., broadcast signals of a broadcasting station broadcasting a music program, and additional broadcast signals of a further transmitter transmitting, for example, digitally coded traffic radio information, then the broadcast frequency mixture received by a receiving antenna, in which the broadcast frequencies of the stations of interest are also included, are split by an antenna signal splitter to the various receivers tuned to the broadcast frequencies of the stations that are of interest.
For this, an antenna signal splitter 120 such as that shown in FIG. 1 is often used, which is made up of a transformer 121 having several windings and a center tap for supplying the antenna signal of receiving antenna 100 and of terminals 125, 126 for coupling out the split antenna signals by the connected receivers and over and above that, resistors 122 shunting the output connectors. By the suitable choice of the resistance value of the resistor(s) 122, namely, for example, in the case of a splitter having two outputs, ideally twice the input impedance of the receiving series, connected to output terminals 125, 126 of splitter 120, which ideally corresponds to the impedance of the antenna signal line, a bidirectional matching of the antenna signal splitter outputs 125 and 126 to the impedance of the system or the respective receiver is achieved. An additional input transformer 123 matches the impedance of antenna 100 or the antenna line to the input impedance of splitting transformer 121.
This circuit is usable in a broadband manner and insensitive to mismatch at individual antenna signal splitter outputs 125, 126. The disadvantage is the attenuation acting in the entire usable frequency range, which of necessity is created by the broadband signal splitting.
Great Britain Patent No. 613927 describes a receiver system having at least two receivers. The receivers are connected to a common antenna via antennal signal lines. Each of the receivers has available a fixed prefilter having bandpass characteristics, so that it has an impedance matching to the antenna signal lines, supplied to them, only in the range of their pass bands lying in different frequency ranges. Each of the receivers is limited to a certain working frequency or a certain narrow working frequency range, in which, as a result of the narrow bandwidths of the prefilters, it has available to it a maximum antenna signal power. Outside the working frequency range, as a result of the narrow bandwidths of the prefilters, practically a total reflection of the antenna signal is present. It is thereby achieved that the antenna signal is available almost loss free to each of the receivers in the frequency range utilized by it.